1. Field of the Invention
The present invention relates to an optical fiber connector for optically connecting an optical fiber and an optical element or an optical fiber, and to an optical communication module using the same.
2. Description of the Related Art
In general, optical communication modules have a combined constitution of optical elements, such as a laser diode and a lens, and an optical fiber connector for connecting optical fibers, and laser beams emitted from the laser diode are focused by the lens so as to be optically coupled in the optical fibers.
Optical fiber connectors in which the optical fibers are detachable to a body of the module are referred to as being of the receptacle type.
The optical fiber connectors include an optical fiber connector of the type connecting optical fibers using screws, and an optical fiber connector of the type connecting optical fibers using elastic fittings.
As shown in FIG. 15, a conventional optical fiber connector 150 includes a housing 151 made of stainless steel. The housing 151 is composed of a plate-like base 151a having a small circular hole 151 formed in the center thereof, and a cylindrical outer peripheral part 151b integrally formed on the base 151a. 
A resin clamper 153 reinforced by glass fiber is composed of a base part 153a, a pair of legs 153c integrally erected on the base part 153a, each having an elastic pawl 153b at an end thereof, and a cylindrical part 153d integrally formed erected on the base part 153a at a position between the legs 153c. The base part 153a is formed with a circular hole 153c having the same size as the circular hole 151c formed in the base 151a. The clamper 153 is accommodated in the housing 151 in such a manner as to superpose the circular hole 151c of the housing 151 and the circular hole 153c of the clamper 153.
A sleeve 155 is composed of a thin-wall long cylindrical part 155a, and a flange 155b integrally formed with a base end of the long cylindrical part 155a. A circular opening 155c is formed at an end of the long cylindrical part 155a, and the inner diameter thereof is accurately formed by cutting from the circular opening 155c to a bottom part 155d of the inner wall of the long cylindrical part 155a. 
The bottom part 155d is formed with an aperture 155e opened through the lower surface of the flange 155b to pass incident or emitted light therethrough. A surface of the bottom part 155d is an abutting surface against which an end surface of an optical fiber (described later) abuts.
The outer periphery of the long cylindrical part 155a is placed in the cylindrical part 153d of the clamper 153 and in the circular hole 151c of the base 151a, and the upper surface of the flange 155b abuts against the lower surface of the base 151a. 
An optical member 160 is composed of an optical element 162, such as a semiconductor laser, a lens 163, and the like. A holder 161 holding therein the optical member 160 is formed in a cylindrical shape, the lens 163 is disposed in the center thereof, the optical element 162 is disposed on one end thereof, and an aperture 161a is formed in the other end for emitting light from the optical element 162 through the lens 163.
The upper surface of the holder 161 having the aperture 161a formed therein is abutted against the lower surface of the flange 155 and is fixed by welding.
As shown in FIG. 14, a plug 101 comprises a plug body 101a, a cylindrical ferrule-holding member 102 accommodated in the plug body 101a, and a ceramic ferrule 103 held in the ferrule-holding member 102.
The ferrule-holding member 102 has a groove-like elastic lock-receiving part 102a formed on an outer peripheral wall thereof, and a circular hole 102b formed in an end thereof for receiving the cylindrical part 153d of the clamper 153 and the sleeve 155 when the plug 101 is fitted to the optical fiber connector 150.
The ferrule 103 contains an optical fiber 100 in advance, and an end surface thereof is polished together with an end surface of the optical fiber 100 so as to be formed in a predetermined shape, and it is mirror-finished.
The ferrule 103 is elastically urged by a coil spring 104 in the plug body 101a in a direction in which an end thereof protrudes outward (leftward in FIG. 14) so as to lock a part of the outer peripheral wall thereof to the inner wall of the ferrule-holding member 102 so that the end of the ferrule 103 is located in the sleeve 155, and is slightly protruding from the end surface of the plug body 101a. 
A method for fitting the plug 101 to the thus-constructed optical fiber 150 will now be described.
First, as shown in FIG. 15, the end of the plug 101 is located to face the opening end of the housing 151 of the optical fiber connector 150.
When the end of the plug 101 is inserted into the opening end of the housing 151, the pair of legs 153c of the clamper 153 abut against the end of the plug 101 and expand, the plug body 101a moves into the housing 151, the outer periphery of the ferrule-holding member 102 moves between the legs 153c, the ferrule 103 moves into the long cylindrical part 155a of the sleeve 155, an end surface of the ferrule 103 is elastically brought into contact with the bottom part (abutting surface) 155d of the sleeve 155, and the pair of elastic pawls 153b of the clamper 153 is snap-fitted into the elastic lock-receiving part 102a. 
As described above, the plug 101 is not easily disconnected from the optical fiber connector 150 by removing operation of the plug 101 because the ferrule 103 is attached in the cylinder of the sleeve 155, and the direction of deformation of the legs 153c is different from the direction of insertion of the plug 101 and the direction of deformation of the elastic pawls 153b. 
Another conventional optical fiber connector (not shown) has been known in which a ferrule is positioned and held by a split sleeve having a screw slot formed by bending a metal plate in a cylindrical shape. A surface of the split sleeve on the opposite side of the screw slot is welded and fixed to the optical fiber connector, whereby the split sleeve is integrally assembled with the optical fiber connector.
In the above-described conventional optical fiber connector 150, since the ferrule 103 of the plug 101 is held in the cylinder of the sleeve 155 of the optical fiber 150 so as to be inserted therein and extracted therefrom, a space is formed between the inner wall of the sleeve 155 and the outer periphery of the ferrule 103. For this reason, since the ferrule 103 moves in the space in the direction perpendicular to an optical axis, the space should be minimized in order to restrict variations in optical coupling due to the insertion and the extraction of the ferrule 103, and a high accuracy is required for forming the inner diameter of the sleeve 155 by cutting.
In another conventional optical fiber connector in which the ferrule is held by the split sleeve, a wide range of welding and fixing conditions for the split sleeve should be ensured in order for the split sleeve to be able to withstand the insertion and extraction of the ferrule. On the other hand, if the range of welding and fixing the split sleeve is broadened, a portion of the split sleeve serving as a spring for holding the ferrule is limited. Therefore, in a ferrule having a small outer diameter, the holding force varies, and the split sleeve becomes difficult to open, so that the ferrule cannot be smoothly inserted in and extracted from the sleeve.